Prior art tensor impedance surfaces using printed-circuit are described in References 1, 2 and 12 below, which are incorporated herein by reference. The impedance surfaces described in those references rely on metal patterns on the printed circuit to provide impedance variation and anisotropy. Such an impedance surface has a number of disadvantages including etching variations, which affect impedance, and limitations on the range of impedance that can be achieved. For example, the ratio of the smallest to the largest impedance may be limited.
Tunable surfaces with varactors are described in Reference 7 below, which is incorporated herein by reference. These tunable surfaces have the disadvantages of cost and complexity because of the required tuning elements, bias lines, and other circuit complexities.
Tensor transmission line metamaterials, as described in Reference 10 below, which is incorporated herein by reference, have the disadvantage that they only apply to transmission line modes. Tensor transmission line metamaterials do not work for or apply to surface waves which have many real-world applications. Transmission line metamaterials may use lumped elements to realize values of epsilon and mu. For example, Reference 10 describes a circuit model that has a shunt element to ground.
Sinusoidally modulated impedance surfaces as described in References 1, 3, 5, and 11 below, which are incorporated herein by reference, have been used to control surface waves in a manner to achieve directive radiation; however, they do not operate well to control polarization.